1. Field of the Invention
The present invention relates to an electrolysis cell assembly of the filter press type having plastic frames and a membrane together with means for sealing the membrane through clamping forces. The invention particularly pertains to such cells suitable for use in the electrolysis of sodium chloride, and in which membranes may be removed and replaced or reactivated and reused individually.
2. Prior Art
As is known to those skilled in the art, a cell frame comprises the basic repeat unit in an electrolytic filter press cell. The cell frame functions as a separator or barrier between the anode of one cell and the cathode of the adjacent cell. A linear series of cathodes, anodes and interposed cell frames constitutes a filter press cell, in toto.
The prior art is repleat with a wealth of technology respecting filter press cells. Generally, however, the prior art has given considerable attention to electrode construction, diaphragm materials and the like. On the other hand, little attention has been directed to the cell frame and to means and methods of sealing diaphragms therein.
In general, in chlor-alkali filter press cells, the chambers are divided by diaphragms or membranes. The diaphragms may be adhered to the cathode screen or affixed by other methods so that alternatives in diaphragm construction have been worked out in a variety of ways. However, membrane sheets are usually spaced closely to or adjacent to the cathode screen and are often sealingly anchored by means other than connection to the cathode screen. Thus, in chlor-alkali membrane filter press cells, this sealing is extremely difficult and critical. One side of the membrane contains hot chlorinated brine which is highly corrosive and prone to seepage and the other side of the membrane contains hot caustic. Leaks of either presents a dangerous safety hazard.
Traditional electrolytic cells are exemplified by diaphragm chlor-alkali cells consisting of an anode base, a cathode can and a top. These are typically sealed to one another by a foam or soft rubber flat gasket. Sealing and electrical insulation are the important functions of the gasket. Spacing between parts is not critical and the diaphragm is deposited on the cathode and thus does not protrude into the sealing area.
In the new membrane filter press cells, gaskets must seal the membrane to the frame and serve also to control the electrode spacing. Conventional filter presses solved the sealing requirement with a caulked recessed design.
U.S. Pat. No. 4,026,782 illustrates the latest prior technology where the membrane is sealed to the frame through a caulked gasket. This patent also shows an auxiliary seal gasket which assists in the prevention of leakage. However, in such arrangements, the membrane is permanently affected by the sealing operation and therefore cannot be satisfactorily regenerated and reused. This is because the membrane generally shrinks during regeneration, and therefore, it will no longer fit the cell.